The transmitter is built on a Printed Circuit Board. This board uses track inductor for L1, L2 and part of L3. The section built around Q1 is the oscillator section. Oscillation frequency is determined by L1, C4 & C5 which forms the tank. Actually C5 is the feedback capacitor. This is required to sustain oscillation. This also influence the operation of tank formed by L1 & C4. Modulation is directly applied to the base of Q1 via C2. A microphone is connected here to serve this purpose. You can alternately feed direct audio here after disconnecting the microphone biasing resistor R1. Q2, Q3 & Q4 gradually raises the output power up to the desired level.

As most of the inductors are PCB etched, there is practically very little frequency drift provided you use a highly regulated and ripple free power supply.

RF output from the transmitter is taken from the junction of C11 & C12. This is unbalanced output of around 75 ohms impedance. But a folded dipole is a balanced type antenna of around 300 ohms impedance. So we need to use a 'BALanced to UNbalanced transformer' or 'BALUN'. A 1:4 type BALUN is employed here for this purpose. Antenna connection is taken from this BALUN via a 300 ohms flat parallel feeder cable commonly used in television to receive terrestrial broadcast. No coaxia is used to feed antenna. This saves cost. Also a parallel feeder cable provides much less signal loss compared to a coaxial.

I've tried to build (make) my own Fm transmitter from the very beginning of my boyhood but failed failed and failed. My first successful Fm transmitter was aired in 2001 when i was a student of class 12. After a long run of 4 years from class 9.

Here's a small FM transmitter ciruit for your desktop or laptop to enjoy the movie and music from a distance. This FM transmitter, which is powered by USB, recovers output on your computer or your MP3 player to the relay on the tape FM (frequency 108 MHz). For Assemblying this FM transmitter kit, an electronics hobbyist will have built in about 30 minutes.

USE DIPOLE ANTENNA FOR MAXIMUM RANGE (COULD BE UP TO 10 KM IN GOOD WEATHER). TUNE BETWEEN 88-108 MHz WITH C5. BB-204 COULD BE REPLACED WITH CONVENTIONAL LED (BIG) WITH REVERSE BIAS (NO LIGHT GIVEN IN CORRECT POLARITY). 9V POWER FOR 2KM WITH GOOD SOUND QUALITY AND GRADUALLY UP TO 18V FOR 10 KM RANGE WITH POOR QUALITY OF SOUND. BEST OF LUCK.

This one is a high power long range (use yagi antenna) FM Transmitter that provides very good frequency stability in about 1km range and very good microphone sensitivity. It can be used inside guitars, as a part of remote control systems or in other similar applications.

The features said above are achieved by including an RF amplifier stage with 10dB gain and AF preamplifier stage to boost the modulation.